Laminated sport bat with internal chamber

ABSTRACT

Sport bat  10 , made of laminated wood  50,  such as of bamboo  51.  Bat  10  includes handle  45 , taper portion  44  and batting portion  30.  Batting portion  30  includes one or more internal chambers  31  for decreasing the weight of bat  10.  Internal chambers  31  may be reinforced with sleeve insert  32,  rubbery coating  34,  or porous filler  33.  Internal chamber  31  is disposed between taper portion  44  and sweet spot  12.

BACKGROUND OF THE INVENTION

[0001] This invention relates to the field of sport bats, and more particularly to sport bats of laminated wood.

BACKGROUND OF THE INVENTION

[0002] Many sport bats, such as for baseball, softball, and cricket, are lathe turned from a single piece of hardwood. Others are made from aluminum. Each type of bat has drawbacks

[0003] Wood bats are not very durable They can splinter during use, which is a safety hazard, as well as disrupting play and costing money. The billets of wood from which the bats are made are inconsistent and often contain hidden flaws that weaken the bat Two bats made from the same lot of wood and with identical dimensions can vary greatly in weight, strength, and hitting power. Sources of good-quality wood for baseball bats are limited and the cut wood billets must be closely inspected before acceptance by a bat maker. The production of highest-quality bats is limited by the wood that is available to the manufacturers

[0004] Aluminum bats are much more durable and uniform than traditional wood bats For these reasons, aluminum bats are often used for school play, although aluminum bats are not allowed in major league baseball play by regulation. Another drawback of aluminum bats is that the sound they make when hitting a baseball is unpleasant to many people The unpleasant ringing sound is due to persistent vibration in the bat, which also frequently causes the player's hands to sting after a hit A major problem is the difficulty of transitioning from an aluminum to a wood bat.

[0005] Baseball bats have been made of other materials, such as fiber-resin composites, but most players agree that they prefer the sound and feel of a wood bat.

[0006] Accordingly, there is a need for a wood bat that is durable and safe, not breaking unpredictably during play. There is a need for a bat can be made inexpensively and does not require special wood and laborious inspection. There is further a need for a bat with traditional sound and feel, but that has design flexibility to allow for adapting the balance, weight, and position of the “sweet spot” to a player's or designer's preferences.

SUMMARY OF THE INVENTION

[0007] This invention is a sport bat, such as a baseball bat, constructed of laminated wood, preferably of laminated bamboo strips. Bamboo is a plentiful and strong wood, typically with a very straight grain Laminated bamboo is a wood product that is more uniform than primal hardwood timbers and can be engineered to vary the stiffness of the laminate as desired.

[0008] Because laminated bamboo is denser than the woods traditionally used for sport bats, the bat of the present invention includes one or more internal chambers to decrease the total weight of the bat. The internal chambers are conveniently formed by omitting certain strips of bamboo from the lay-up of the laminated billet, according to a pre-planned lay-up schedule.

[0009] The internal chambers both decrease total weight and move the center of gravity of the bat toward the end opposite the handle. The preferred location of the internal chambers is below, that is, toward the handle from, the “sweet spot.” The internal chambers also function by “enlarging the sweet spot” and dampening vibration. The sweet spot will be discussed in more detail below.

[0010] Each internal chamber may preferably be reinforced with a sleeve insert, a rubbery coating on the interior wall of the chamber, or by lightweight shock-absorbent material filling the chamber.

[0011] The bamboo strips are laid up around the sleeve insert, if used, to form a blank, or billet, of at least the length and diameter of the finished baseball bat. After the adhesive used for lamination has been cured, the billet is turned on a lathe to produce the rough baseball bat An end cap is preferably attached to the end of the bat and the bat is sanded and finished as desired

[0012] The baseball bat according to the present invention has a traditional sound and feel at impact. However, the bat of the present invention is more durable and reliable than traditional wood bats The bat is made inexpensively from a plentiful material and has far more design flexibility than a one-piece wood bat. The bat of the present invention is well-damped for vibration and does not sting the hands of the batter.

[0013] The invention will now be described in more particular detail with respect to the accompanying drawings in which like reference numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a preferred embodiment of the sport bat, shown in longitudinal cross-sectional view

[0015]FIG. 2 is an alternative embodiment of the sport bat, shown in longitudinal cross-sectional view and partly cut away.

[0016]FIG. 3 shows the laid-up billet from which the sport bat of FIG. 1 will be cut.

[0017]FIG. 4 is a transverse cross-sectional view of the billet of FIG. 3, taken along line 4-4.

DETAILED DESCRIPTION OF THE INVENTION

[0018]FIG. 1 is a preferred embodiment of the sport bat 10, such as a softball or baseball bat 11, shown in longitudinal sectional view An alternative embodiment of baseball bat 11, also shown in longitudinal sectional view, is shown in FIG. 2.

[0019] Baseball bat 11 generally includes an elongate body 20 with a longitudinal axis 21. Body 20 includes a handle 45 for gripping, a batting portion 30, and taper portion 44 between handle 45 and batting portion 30. Batting portion 30 is cylindrical and is for striking a sports ball.

[0020] It is well known that striking, or hitting, a ball with a bat typically causes vibration in the bat. The vibration can be severe enough to sting the hands of the person batting It is also well known that some hits do not result in vibration being felt in the hands of the batter Such hits also tend to result in the ball traveling especially far and fast. There are various hypotheses of what causes this phenomenon; one especially credible explanation is the “acoustic” theory of Rod Cross as cited by Daniel Russell.

[0021] The acoustic explanation involves the fact that a typical ball bat has three main vibrational bending modes that are activated when as ball is struck Cross defines the zone between the [farthest from the handle] nodes of the first and second modes of vibration as the “sweet zone”, analogous to what is traditionally called the “sweet spot”, a point on the bat that yields strong hits without vibration of the hands. Herein this zone will be called sweet spot 12 Sweet spot 12 can be empirically located by suspending the handle of the bat from the fingers and tapping the length of batting portion 30 until the minimum of vibration is felt in the fingers. Russell's more analytical method is to suspend a bat with an attached accelerometer and strike the bat at many different points. Modal analysis is done on the accelerometer data to determine the shapes and frequencies of the various vibrational modes.

[0022] Batting portion 30 includes one or more internal chambers 31 that decrease the weight of bat 10, shift the center of mass of bat 10, and influence the location and width of sweet spot 12 The embodiment of FIG. 1 includes one internal chamber 31 and the embodiment of FIG. 2 includes three internal chambers 31. It has been found that for baseball bat 11, one or more internal chambers 31 with total volume of two to six cubic inches will reduce the weight of baseball bat 11 to within the desired range.

[0023] It is preferred that internal chambers 31 be located between taper portion 44 and sweet spot 12. Sweet spot 12 may be located empirically, as discussed above, but in general, it has been found that sweet spot 12 is five inches or less from distal end 40 of body 20.

[0024]FIG. 3 shows the laid-up billet 53 from which the bat of FIG. 1 will be cut FIG. 4 is a transverse cross-sectional view of billet 53 of FIG. 3, taken along line 4-4 Dashed line 10′ indicates the outline of bat 10 that will be lathe cut from billet 53.

[0025] Billet 53 is formed from sticks 52 of bamboo or other suitable wood. Sticks 52 are dipped into an adhesive 55, such as epoxy, and stacked into the size and shape of billet 53 required. Sticks 52 may be added to the assembly in a freeform manner or may be laid into a mold, or by other techniques as are well known to those skilled in the art

[0026] Bat 10 is preferably made from laminated wood 50, such as laminated bamboo strips 51. Laminated bamboo 51 is a strong, durable material, but denser than most woods used for traditional baseball bats. To decrease the weight of bat 10, internal chamber 31 must have a density less than that of laminated wood 50 or laminated bamboo 51

[0027] In the preferred embodiment of FIG. 1, internal chamber 31 is a simple void in laminated bamboo 51, having a wall 36 enclosing internal space 35, which is filled with air. Wall 36 includes an upper end 37 and a lower end 38. In the alternative embodiment of FIG. 3, internal chamber 31 includes sleeve insert 32 to reinforce internal chamber 31 against collapse Sleeve insert 32 may be of metal, graphite, or plastic Although metal is denser than laminated bamboo 51, the combination of metal sleeve insert 32 and the air of internal space 35 has a density less than that of laminated bamboo 51.

[0028] Sleeve insert 32 may be circular, square, rectangular, or other shape in cross section. A sleeve insert 32 that is square or rectangular in cross section fits most snugly into a chamber 31 that is formed by omitting certain sticks 52 from the billet. A sleeve insert 32 that is circular or other shape in cross section should have sticks 52 that are tangent to three or more segments on the perimeter of sleeve insert 32 such that sleeve insert 32 does not rattle or shift within internal chamber 31 Some small voids will likely be present between chamber wall 36 and some parts of a sleeve insert 32 that is non-rectangular in cross section, but this is not detrimental to the performance of bat 10.

[0029] Sleeve insert 32 is shown as a hollow pipe in the figures, but sleeve insert 32 could alternatively be a solid piece of graphite, plastic, or foam. The main requirement for sleeve insert 32 is that the density of the material used be low enough to decrease the weight of baseball bat 11 to the desired total weight and balance. It is also desirable that sleeve insert 32 absorb or dampen shock and vibration.

[0030] Internal chamber 31 may alternatively include a rubbery coating 34 on chamber wall 36, as shown in FIGS. 3 and 4 Rubbery coating 34 is easily introduced during lay-up of billet 53 by dipping one side of each of sticks 52 that enclose internal chamber 31.

[0031] In the preferred embodiment shown in FIG. 2, multiple internal chambers 31 are filled with a porous filler 33, such as an elastomeric foam, such as polyurethane foam, or a fibrous material, such as jute. Porous filler 33 must have a lower density than laminated wood 50 or laminated bamboo 51. It is desirable that porous filler 33 absorb or dampen shock and vibration.

[0032] Although particular embodiments of the invention have been illustrated and described, various changes may be made in the form, composition, construction, and arrangement of the parts herein without sacrificing, any of its advantages. Therefore, it is to be understood that all matter herein is to be interpreted as illustrative and not in any limiting sense, and it is intended to cover in the appended claims such modifications as come within the true spirit and scope of the invention. 

I claim:
 1. A sport bat having a longitudinal axis and a sweet spot, including: a body, including a handle; a taper portion attached above said handle, and a batting portion attached above said taper portion, including: an internal chamber that decreases the weight of said sport bat; including: an internal space, and a wall surrounding said internal space; including:  a bottom end disposed above said taper portion; and  a top end disposed below said sweet spot.
 2. The sport bat of claim 1, said internal chamber including: a sleeve insert in contact with said wall for reinforcing said internal chamber.
 3. The sport bat of claim 1, said internal chamber including: a shock absorbing coating on said wall
 4. The sport bat of claim 1, said internal chamber including: a porous filler.
 5. The sport bat of claim 1, said body being fabricated from laminated wood
 6. The sport bat of claim 5, the laminated wood being strips of bamboo attached together with adhesive.
 7. The sport bat of claim 1, said batting portion including a plurality of chambers disposed between said taper portion and said sweet spot
 8. The sport bat of claim 2, said sleeve insert being made from metal, graphite, or plastic.
 9. A baseball bat having a longitudinal axis and a sweet spot, including a body, including: a handle; a taper portion attached above said handle; and a batting portion attached above said taper portion; including. an internal chamber that decreases the weight of said baseball bat, including: an internal space; and a wall surrounding said internal space, including:  a bottom end disposed above said taper portion; and  a top end disposed below said sweet spot, and a distal end opposite said taper portion.
 10. The baseball bat of claim 9, said body being fabricated from laminated wood.
 11. The baseball bat of claim 10, the laminated wood being strips of bamboo attached together with adhesive.
 12. The baseball bat of claim 11, said top end disposed at least five inches from said distal end
 13. The baseball bat of claim 11, said internal chamber including: a sleeve insert in contact with said wall for reinforcing said internal chamber.
 14. The baseball bat of claim 11, said internal chamber including: a shock absorbing coating on said wall.
 15. The baseball bat of claim 11, said internal chamber including: a porous filler.
 16. The baseball bat of claim 11, said batting portion including a plurality of internal chambers.
 17. The baseball bat of claim 11, said internal space having a total volume in the range of 2 to 6 cubic inch 